The Confined Hard Disk Two Piston System simulates a constant-energy two-dimensional system of unit mass particles confined by two frictionless pistons of equal mass M.   This computer model complements theoretical work describing the adiabatic expansion of an ideal gas using the quasi-static approximation.  Users can set the number of particles  N, their diameter and their initial particle kinetic energy.  Slow-moving particles are color-coded as blue and fast particles are color-coded as yellow.  The time evolution of temperature, pressure, and piston speed are shown in a second window.
 
Particles in this model have unit mass and interact through contact forces.  Collision times are computed analytically because particles and pistons move with constant velocity between collisions. The time evolution algorithm advances the particle position from collision to collision until the requested time step is achieved.  The time evolution is then paused, data is accumulated, and the screen is redrawn.

The Confined Hard Disk Two Piston System is a supplemental simulation for the article "Evolution of ideal gas mixtures confined in an insulated container by two identical pistons" by Joaquim Anacleto, Joaquim Alberto C. Anacleto, and J. M. Ferreira in the American Journal of Physics 79(10), 1009-1014 (2011) and has been approved by the authors and the American Journal of Physics (AJP) editor.  This model was developed using the Easy Java Simulations (Ejs) modeling tool.  It is distributed as a ready-to-run (compiled) Java archive.  Double clicking the  ejs_stp_hd_ConfinedHardDiskTwoPistonSystem.jar file will run the program if Java is installed.

Please note that this resource requires at least version 1.5 of Java.